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Tsirkin" , Paolo Abeni , Sasha Levin Subject: [PATCH 6.1.y 3/3] vhost/vsock: size receive SKBs from declared payload Date: Sat, 14 Nov 2026 19:30:08 -0500 Message-ID: <20261115002958.559603-3-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261115002958.559603-1-sashal@kernel.org> References: <20261109201916-failed-6.1-d5e912448cd9@kernel.org> <20261115002958.559603-1-sashal@kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Daehyeon Ko <4ncienth@gmail.com> [ Upstream commit d5e912448cd98b261eba8e35ab838f2dc69a79f5 ] vhost_vsock_alloc_skb() sizes the skb from iov_length(), the total guest descriptor length. virtio_transport_inc_rx_pkt() instead adds hdr->len to rx_bytes and buf_used, and budgets each queued skb as SKB_TRUESIZE(0). The guest controls the descriptor length and hdr->len independently. A guest can therefore provide a 64 KiB descriptor while declaring a zero payload. The descriptor-sized skb remains queued, rx_bytes and buf_used remain unchanged, and only the fixed queue-entry budget limits retention. This is not a lifetime leak: the skb is freed when dequeued or at socket teardown. Repeating this across connections can nevertheless exhaust host memory. On Linux v7.2, 455 such descriptors retained 30,255,680 bytes for a 262,144-byte receive buffer; a full-payload control retained 265,984 bytes. Vhost previously read hdr->len and allocated pkt->buf from that value. The conversion from virtio_vsock_pkt to sk_buff instead allocated receive skbs from the descriptor length, introducing the allocation-accounting mismatch. Copy the header into a stack object and validate hdr->len before allocating the skb. Size the allocation as sizeof(hdr) + payload_len so descriptor capacity no longer determines queued memory. Check payload_len against len - sizeof(hdr) to avoid addition overflow on 32-bit hosts. Fixes: 71dc9ec9ac7d ("virtio/vsock: replace virtio_vsock_pkt with sk_buff") Cc: stable@vger.kernel.org Signed-off-by: Daehyeon Ko <4ncienth@gmail.com> Reviewed-by: Stefano Garzarella Acked-by: Michael S. Tsirkin Link: https://patch.msgid.link/20261004235101.1464007-1-4ncienth@gmail.com Signed-off-by: Paolo Abeni Signed-off-by: Sasha Levin --- drivers/vhost/vsock.c | 34 ++++++++++++++++------------------ 1 file changed, 16 insertions(+), 18 deletions(-) diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c index 1fc03038e5543..43533ae6ce211 100644 --- a/drivers/vhost/vsock.c +++ b/drivers/vhost/vsock.c @@ -327,7 +327,7 @@ static struct sk_buff * vhost_vsock_alloc_skb(struct vhost_virtqueue *vq, unsigned int out, unsigned int in) { - struct virtio_vsock_hdr *hdr; + struct virtio_vsock_hdr hdr; struct iov_iter iov_iter; struct sk_buff *skb; size_t payload_len; @@ -344,34 +344,32 @@ vhost_vsock_alloc_skb(struct vhost_virtqueue *vq, if (len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE + VIRTIO_VSOCK_SKB_HEADROOM) return NULL; - /* len contains both payload and hdr */ - skb = virtio_vsock_alloc_skb(len, GFP_KERNEL); - if (!skb) - return NULL; - iov_iter_init(&iov_iter, ITER_SOURCE, vq->iov, out, len); - hdr = virtio_vsock_hdr(skb); - nbytes = copy_from_iter(hdr, sizeof(*hdr), &iov_iter); - if (nbytes != sizeof(*hdr)) { + nbytes = copy_from_iter(&hdr, sizeof(hdr), &iov_iter); + if (nbytes != sizeof(hdr)) { vq_err(vq, "Expected %zu bytes for pkt->hdr, got %zu bytes\n", - sizeof(*hdr), nbytes); - kfree_skb(skb); + sizeof(hdr), nbytes); return NULL; } - payload_len = le32_to_cpu(hdr->len); + payload_len = le32_to_cpu(hdr.len); + + /* The pkt is too big or the length in the header is invalid */ + if (payload_len > len - sizeof(hdr)) + return NULL; + + /* Allocate only for the payload declared in the header. */ + skb = virtio_vsock_alloc_skb(payload_len + sizeof(hdr), GFP_KERNEL); + if (!skb) + return NULL; + + memcpy(virtio_vsock_hdr(skb), &hdr, sizeof(hdr)); /* No payload */ if (!payload_len) return skb; - /* The pkt is too big or the length in the header is invalid */ - if (payload_len + sizeof(*hdr) > len) { - kfree_skb(skb); - return NULL; - } - virtio_vsock_skb_put(skb, payload_len); nbytes = copy_from_iter(skb->data, payload_len, &iov_iter); -- 2.53.0